1. Field of the Invention
The invention relates to collimators for use with DWDM multiplexor or demultiplexor, and particularly to dual fiber collimators with V-groove positioning devices.
2. The Related Art
As well known, Dense-Wavelength-Divison-Multiplexing (DWDM) multiplexor or demultiplexor generally use the optical filter and the fiber optic collimators. In these applications, a band-pass optical filter is employed to multiplex or demultiplex a desired transmission channel of the in-and-out light of the system according to its center wavelength. An international standard wavelength grid has been suggested by International Telecommunication Union (ITU) for the center wavelengths of the DWDM channels. In the DWDM application, the center wavelength of the DWDM optical filter which does not coincide with the ITU standard wavelength, should be tuned to comply therewith. As the center wavelength of the band-pass optical filter depends upon the incident angle of the light that propagates therein, the center wavelength of the band-pass optical filter can be tuned by such an incident angle. The prior art generally uses an Y-branch structure of the three conventional fiber optic collimators wherein the incident angle is tuned by changing the angles between the collimators and thus the center wavelength of such a multiplexor/demultiplexor is adjustably coincident with the desired ITU wavelength. The disadvantage of such design includes difficulties in reducing its size to achieve a robust and compact structure. The related matters may be referred to U.S. Pat. Nos. 4,464,022, 5,204,771, 5,574,596 and 5,845,023, and "compact Polarization-Independent Optical Circulator", Applied Optics, Vol. 20, No. 15, August 1981, pp. 2683-2687.
Therefore, it is desired to provide a collimator with means which can precisely and efficiently have the filter and the corresponding collimated beam with a required incident angle, thus assuring a desired ITU wavelength can be obtained.